1. Field of the Invention
The present invention relates to a process for the production of sintered films of Cd.sub.1-x Zn.sub.x S (0.ltoreq.x&lt;1) having high optical transmittance which may be used for window layers in solar cells. More particularly, the invention relates to a process for preparing sintered films under a ZnCl.sub.2 atmosphere. The process may include the step of resintering films which have first been sintered under a ZnCl.sub.2 atmosphere.
2. Description of the Prior Art
It is well known in the art of film type solar energy cells, such as CdTe, CuInSe.sub.2, Cu.sub.2 S and the like to use different semiconductor films having an energy gap (band gap) greater than that of the light absorbing layer (CdTe, etc.) and that improved optical transmittance considerably enhances the performances of such cells. (References 1-3) Cd.sub.1-x Zn.sub.x S is useful as a window material, and its energy gap and lattice constant may vary depending upon the composition thereof, that is, at different values of x. (Reference 4) Many methods for obtaining sintered films x is 0 (i.e., CdS) have been devised and proposed. (References 5,6) However, these methods do not apply to the production of the sintered films of Cd.sub.1-x Zn.sub.x S having high optical transmission wherein x is greater than 0. (Reference 7)
The above references 1-7 are incorporated into this specification as a part of the present invention. These references are identified in the detailed description of the preferred Embodiments.
In general, the sintered film of CdS (x=0) is prepared by adding a suitable binder to a mixture of CdS power and CdCl.sub.2 powder to form a paste composition, and applying the paste onto a proper substrate, followed by sintering thereof at a high temperature. However, when a sintered film of Cd.sub.1-x Zn.sub.x S is prepared by adding ZnS powder at the stage of the initial compounding of the paste in the same manner as in the method of producing the sintered film of CdS, an undesirable microscopic structure is created and, thus, it is difficult to obtain sintered films with high optical transmittance.